1. Field of the Invention
This invention relates to a process for oxidizing cyclohexane with air whereby adipic acid precursors are prepared which permit improved yield of adipic acid. More specifically, this invention relates to a process for oxidizing cyclohexane with air to obtain adipic acid precursors by conducting said oxidation in the presence of a binary catalyst system of chromium and cobalt compounds.
2. Description of the Prior Art
In U.S. Pat. No. 3,530,185 there is disclosed a process for manufacturing precursors of adipic acid by oxidation of cyclohexane with an oxygen-containing inert gas which process is conducted at elevated temperature and pressure by contacting a stream of liquid cyclohexane at each of several successive stages of an oxidation zone with a mixture of gases including molecular oxygen at controlled partial pressure and inert gas; causing said mixtures of gases to pass countercurrent to the stream of cyclohexane; and recovering the stream of cyclohexane containing partial oxidation products of cyclohexane from the last of said stages. The useful partial oxidation products of cyclohexane, i.e. adipic acid precursors, which are the primary products of said process comprise cyclohexanol and cyclohexanone. Under the conditions of this process, conversion to by-products such as dicarboxylic acid and monocarboxylic acids is minimized.
In U.S. application Ser. No. 365,225, filed May 30, 1973 there is disclosed a process for the oxidation of cyclohexane to a product fluid consisting essentially of unreacted cyclohexane, cyclohexanone, cyclohexanol and a high proportion of cyclohexyl hydroperoxide, the product fluid being substantially free of peroxides other than cyclohexylhydroperoxide. This process comprises oxidizing cyclohexane containing a cobalt catalyst in a series of zones wherein cyclohexane is fed countercurrent to an oxidizing gas containing molecular oxygen, the amount of oxygen present in each reaction zone being in excess of that which will react under the particular conditions of that zone. The catalyst level required is from about 0.1 to 5 ppm based on the product fluid defined as the fluid recovered exiting the lowest oxidation zone and containing cyclohexane, cyclohexanol, cyclohexanone, cyclohexylhydroperoxide and other oxidation products in minor amounts. More catalyst than 5 ppm cobalt results in significantly lower amounts of cyclohexylhydroperoxide. At catalyst levels lower than 0.1 ppm the reaction becomes inefficient in that by-products including peroxides other than cyclohexylhydroperoxide are produced while lowering productivity of the desired products.